1,4-Benzodioxanes. I. Synthesis involving the reaction of .alpha.-halo Michael acceptors with catechol

Abstract

Halo Michael acceptors react with catechol in aprotic solvents in the presence of potassium carbonate to form 2-substituted 1,4-benzodioxanes. Cis 0-alkyl and 0-alicyclic -halo Michael acceptors yield primarily cis 2,3-disubstituted 1,4-benzodioxanes, whereas trans 2,3-disubstituted isomers predominate when catechol is treated with trans 0-alkyl -halo Michael acceptors. It is therefore inferred that the reaction proceeds via a cis Michael addition of catechol monoanion, followed by intramolecular nucleophilic displacement of halide from the newly generated sp3 a carbon by the remaining catechol oxygen. Ethyl l,4-bromobut-2-enoate, formed by isomerization of ethyl 2-bromobut-2-enoate during the course of the reaction of the latter with catechol, is believed to be the source of the isomeric ethyl l,4-benzodioxanyl-2-acetate isolated as a minor product.

How Reaction Conditions May Influence the Regioselectivity in the Synthesis of 2,3-Dihydro-1,4-benzoxathiine Derivatives

“…The mechanism of this reaction was abundantly studied few decades ago firstly by Koo and coworkers 21 and later by Caputo's research group. 22 They strengthened the hypothesis of the initial dehydrobromination of the 2,3-dibromopropionate, achieving the 2-bromoacrylate, and the consecutive Michael addition of the cathecol anion on the primary carbon. Similarly, considering this simple procedure, we decided to apply it on 1,2-mercaptophenol instead of catechol, treating the 2-hydroxythiophenol with methyl or ethyl 2,3-dibromopropionate, in presence of triethylamine (TEA) as weak organic base.…”

“…The mechanism of this reaction was abundantly studied a few decades ago, first by Koo and co-workers and later by Caputo’s research group . They strengthened the hypothesis of the initial dehydrobromination of the 2,3-dibromopropionate, achieving the 2-bromoacrylate, and the consecutive Michael addition of the cathecol anion on the primary carbon.…”

Complete isolation and characterization of silybins and isosilybins from milk thistle (Silybum marianum)Electronic supplementary information (ESI) available: HPLC chromatograms of isolates and extracts. See http://www.rsc.org/suppdata/ob/b3/b300099k/

“…In the 1 H NMR spectrum, the coupling constant of H-β (7.9 Hz) suggested that the two methine protons could be in as a trans configuration. 50, 51 Proton signals of a hydroxymethylene moiety at δ 3.52 and 3.33 (H-γ) were observed, and one of them (δ 3.52) was long-range correlated with a methine carbon signal at δ 75.9 (C-β). These observations indicated the presence of a lignan moiety, and this was confirmed by a TOCSY experiment where proton signals H-2Љ, H-5Љ, and H-6Љ were correlated with H-α and H-β to become a network.…”

A reinvestigation of the synthesis of cis-1,2,3,4,4a,10a-hexahydro[1,4]benzodioxino[2,3-c]pyridine and a synthesis of meso-2,3,4,5,5a,11a-hexahydro-1H-[1,4]benzodioxino[2,3-d]azepine

“…Found: C, 55.44; , 6.19; N, 5.00. meso-2,3,4,5,5a,lla-Hexahydro[l,4]benzodioxino [2,3-d]azepine (14). Crude N-methylsulfonyl [1,4]benzodioxinoazepine 13 (37.1 g, 0.131 mol) was dissolved in benzene (200 mL) and added during 15 min to a well-stirred solution of Red-al (Aldrich Chemical Co.) (191 mL of a 70% solution, 0.66 mol) in benzene (250 mL). The mixture was refluxed for 4 h and then allowed to stand overnight at room temperature.…”